We will investigate the impact of four frequently abused substances (marijuana, caffeine, alprazolam and alcohol) on work related performance. Comparisons of diverse dosages of these drugs with placebo will employ a series of double-blind cross-over experiments. Caffeine withdrawal effects will also be investigated. While data on a range of tasks are to be collected, emphasis is placed on performance in a unique experimental simulation setting that provides validated information on functioning in white collar occupations. The proposed research is designed 1. to examine the effects of substance use and abuse (marijuana, caffeine, alprazolam and alcohol) on various aspects of white collar task performance, 2. to elucidate possible relationships between blood levels and complex performance, 3. to determine the effects of substance dosage on complex task performance, 4. to determine the effects of substance withdrawal on task performance, 5. to determine the extent to which parallels in the effects of substances on simpler and on more complex aspects of performance exist. A third stimulation scenario will be modified (as needed) and validated to provide for more efficient comparison of within treatment (e.g., two drug levels vs. placebo) conditions in research on items 1 through 5 as applicable.